This invention relates to the recovery of ammonia or an amine from a resin bed comprising the alkali metal and ammonium or amine salts of a strong acid cation exchange resin.
In the production of power, such as in a steam turbine system wherein large amounts of water are converted to steam and subsequently condensed, to reduce the corrosive effect of the water supplied for steam generation, the pH of the water is adjusted to above about 9 by the addition of ammonia. In addition, the water is required to be free of solid content, the presence of which produces surface coatings within the turbine, boiler and conduits and otherwise deleteriously affects power production. Although the condensed water (hereinafter "condensate") is recycled through the system, solid forming precursors, particularly alkali metal solutes such as sodium ions, are introduced into the system by the addition of make-up water, leakages, corrosion of metals and the like.
To remove such solid forming precursors, the condensate, including any make-up feed water, is purified in a condensate polishing operation. Such operation conventionally consists of contacting the condensate with both anion and cation exchange resins, typically a mixed resin bed containing a mixture of a strong acid cation exchange resin and a strong base anion exchange resin or with separate resin beds, wherein one bed contains a strong acid cation exchange resin and a second bed contains a strong base anion exchange resin or a mixture of anion and cation exchange resins. In operation, the cations in solution such as sodium or ammonium ions are exchanged for the cations, typically hydrogen, on the cation exchange resin. Similarly, anions in solution are exchanged with the anions, typically hydroxide, on the anion exchange resin.
Upon exhaustion of the resins, e.g., the reduction in the capacity of the resins to a commercially impractical level, the anion and cation resins are separated and the separated resins regenerated. The anion exchange resin is conventionally regenerated employing techniques such as described in U.S. Pat. Nos. 3,385,787 and 3,501,401.
Typically, the exhausted cation resin is regenerated using a strong mineral acid such as sulfuric or hydrochloric acid as the regenerant. Upon regeneration, hydrogen displaces the alkali metal and ammonium or amine ions on the cation exchange resin, converting the resin to hydrogen form. The alkali metal and ammonium or amine ions exit from the resin bed with the regenerant solution. The relatively high concentration of alkali metal ions in the exiting regenerant solution precludes the reuse thereof within the power production facility. Thus, the exiting regenerating solution is conventionally sent to waste. Unfortunately, the ammonium or amine ions in this solution, which ions are usefully employed in reducing the corrosive effects of the condensate, are also wasted. Thus, relatively large amounts of ammonia must be added to the system to impart the required pH to the condensate. Moreover, pollution problems are often associated with the disposal of the solution containing the ammonium or amine ions.
Therefore, in view of the expense incurred in not reusing the ammonia and the problems associated with its disposal, it would be highly desirable to provide a method for recovering the ammonia or amine from a resin bed comprising a cation exchange resin having both ammonium or amine and alkali metal cations attached thereto.